They already had 32bit Win32 Windows on Windows (WoW) subsystems on all machines, even ARM64 to a point - the only thing I've seen that it didnt run out of the box was OpenGL which they have a (??!) Store app for Maya3d or something that does OpenGL to DirectX translation - and that seemed to work OK. The biggest issues I had with Windows on ARM64 was the lack of cooling.

Back on track - the 16 bit DOS and Windows stack is a lot different than Win32 - totally different windowing, drawing to the screen, and memory management is involved - it was probably pulled for security reasons and the most common one at Microsoft - "the guy who maintained this left or retired"